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The synthesis of Co‐doped Mn3O4 nanocubes was achieved via galvanic replacement reactions for photo‐reduction of CO2. Co@Mn3O4 nanocubes could efficiently photo‐reduce CO2 to CO with a remarkable turnover number of 581.8 using [Ru(bpy)3]Cl2 ⋅ 6H2O as photosensitizer and triethanolamine as sacrificial agent in acetonitrile and water. The galvanic replaced Co species are homogeneously distributed at the outer surface of Mn3O4, providing catalytic active sites during CO2 reduction reactions, which facilitate the separation and migration of photogenerated charge carriers, further benefiting the outstanding photocatalytic performance of CO2 reduction. Density functional theory calculations revealed that the decreasing of conduction band maximum in Co@Mn3O4 was beneficial to the electron attachment from the excited sensitized molecule, which promoted photocatalytic reduction of CO2. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of nitrogen to produce ammonia at moderate conditions in aqueous solutions holds great prospect but also faces huge challenges. Considering the high selectivity of Au‐based materials to inhibit competitive hydrogen evolution reaction (HER) and high activity of transition metals such as Fe and Mo toward the nitrogen reduction reaction (NRR), it was proposed that Au‐based alloy materials could act as efficient catalysts for N2 fixation based on density functional theory simulations. Only on Mo3Au(111) surface the adsorption of N2 is stronger than H atom. Thermodynamics combined with kinetics studies were performed to investigate the influence of composition and ratio of Au‐based alloys on NRR and HER. The binding energy and reorganization energy affected performance for the initial N2 activation and hydrogenation process. By considering the free‐energy diagram, the computed potential‐determining step was either the first or the fifth hydrogenation step on metal catalysts. The optimum catalytic activity could be achieved by adjusting atomic proportion in alloys to make all intermediate species exhibit moderate adsorption. Free‐energy diagrams of N2 hydrogenation via Langmuir‐Hinshelwood mechanism and hydrogen evolution via Tafel mechanism were compared to reveal that the Mo3Au surface showed satisfactory catalytic performance by simultaneously promoting NRR and suppressing HER. Theoretical simulations demonstrated that Au‐Mo alloy materials could be applied as high‐performance electrocatalysts for NRR. [ABSTRACT FROM AUTHOR]

The pH‐dependent surface‐enhanced Raman spectra of two typical surface sensor molecules p‐mercaptobenzoic acid (PMBA) and p‐mercaptopyridine (PMPY) were simulated by density functional theory calculations. First, the acid dissociation constants and individual surface Raman spectra of PMBA and PMPY were computed and compared with experimental results. It was found that acid dissociation constants calculated by the hybrid implicit‐explicit model and surface‐enhanced Raman scattering (SERS) spectra simulated by the explicit model most closely coincide with experimental results. Then, the pH‐dependent SERS spectra of PMBA and PMPY were obtained by overlaying the SERS of individual acid species and base species multiplied by their molar fractions, which were calculated from the acid dissociation constants. During the deprotonation process of PMBA, the Raman intensity from COOH stretching decreases and the Raman intensity from COO− stretching increases. During the protonation process of PMPY, the ν8a mode undergoes a significant blueshift and the relative Raman intensity of ν7a mode decreases. At last, pH calibration curves of PMBA and PMPY were obtained according to the simulated pH‐dependent Raman spectra, in which the logarithmic value of relative Raman intensity of characteristic peaks varies almost linearly with solution pH. [ABSTRACT FROM AUTHOR]

Abstract: Conjugated carbonyl compounds have become the most promising type of organic electrode materials for rechargeable Li‐ion batteries because only they can achieve simultaneously high energy density, high cycling stability, and high power density. In this work, we have performed first‐principles density functional theory (DFT) calculations to explore the fundamental rules of how the electronic structure and redox properties of a typical conjugated carbonyl compound, phenanthrenequinone (PQ), are modified by adjusting the heteroaromatic building blocks. Such a molecular design strategy allows for the improvement in discharge potential while the specific capacity remains nearly unchanged. The correlation between the electronic structures and redox properties for the designed PQ derivatives is systematically discussed. It is demonstrated that the discharge potential of the PQ derivatives depends strongly on the frontier orbital levels, the electric potential, and the Li‐bonding configurations. The electrostatic potential (ESP) maps show visible displays of molecular electric structures and can be applied to understand how the redox properties of the PQ derivatives are modified by the heteroaromatic building blocks. [ABSTRACT FROM AUTHOR]

The synthesis of aromatic azo compounds from anilines and nitrobenzene usually requires environmentally unfriendly transition metal catalysts. Here, we propose that azobenzene oligomers are formed in surface-enhanced Raman experiments assisted by surface plasmon resonance. The photocatalytic polymerization of p-dinitrobenzene (DNB) and p-phenylenediamine (PDA) to the corresponding azo-like oligomers on silver surfaces is studied by the surface-enhanced Raman spectroscopy and density functional theory. First, the normal Raman and surface Raman spectra of DNB and PDA are simulated and measured. The simulated normal Raman spectra are in good agreement with their solid-state Raman spectra. However, the simulated surface Raman spectra of DNB-Ag10 and PDA-Ag10 complexes are significantly different from the experimental surface-enhanced Raman spectra. We propose that DNBs has a reductive coupling and PDAs undergo an oxidative coupling reaction during SERS experiments. Secondly, the Raman spectra of the possible NN coupling oligomers of DNB and PDA are simulated. They are compared with the SERS spectra of DNB and PDA adsorbed on silver surfaces. Especially, the Raman spectra of p, p′-dinitroazobenzene and p, p′-diaminoazobenzene are in good agreement with the SERS spectra of DNB and PDA adsorbed on silver surface. Finally, two reaction mechanisms are proposed to explain the surface photocatalysis of DNB and PDA. In the solution, the nitro group of DNB can be reduced by the excited hot electrons. DNBs are then converted to p, p′-dinitroazobenzene through multiple proton and electron transfers. In the air and in the presence of O2, O2 is firstly activated through surface plasmon resonance. PDAs are then converted to p, p′-diaminoazobenzene by the generated active oxygen species. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Surface plasmon resonances (SPRs) have been found to promote chemical reactions. In most oxidative chemical reactions oxygen molecules participate and understanding of the activation mechanism of oxygen molecules is highly important. For this purpose, we applied surface-enhanced Raman spectroscopy (SERS) to find out the mechanism of SPR-assisted activation of oxygen, by using p-aminothiophenol (PATP), which undergoes a SPR-assisted selective oxidation, as a probe molecule. In this way, SPR has the dual function of activating the chemical reaction and enhancing the Raman signal of surface species. Both experiments and DFT calculations reveal that oxygen molecules were activated by accepting an electron from a metal nanoparticle under the excitation of SPR to form a strongly adsorbed oxygen molecule anion. The anion was then transformed to Au or Ag oxides or hydroxides on the surface to oxidize the surface species, which was also supported by the heating effect of the SPR. This work points to a promising new era of SPR-assisted catalytic reactions. [ABSTRACT FROM AUTHOR]